Remove 'a from wordLang AST onwards

@myreen pointed out that the only use of 'a in the AST (from wordLang onwards) is for constants.

It should be possible to represent these with nums instead, and have the entire compiler be non-dependent on 'a.

However, this is a very expensive refactor (the semantics still needs to know 'a, and some compiler passes will need to change so that they depend on a word size config).

Start by mapping the wordLang AST and compiler passes that still depend on 'a, then compare them with the semantics, which the issue says still needs 'a. Identify how constants could use nums and where passes would need a word-size configuration. Done means the compiler from wordLang onward no longer depends on 'a while the stated semantics dependency remains understood.

Written by the indexing model from the issue text.